Detonation indicating system



Feb. 25, 1947. A. CROSSLEY ETAL 2,416,614

DETONATION INDICATING SYSTEM `Filed Aug. 12, 1943 27(067572715 4 /e ,ZW/'all VNQ.

Pnenfea Feb. 25, 1947 DETONATIONINDICATING SYSTEM Alfred Crossley, Evanston, and David L. Elam,

Roselle, Crossley Ill.;

said Elam assignor to said Application August 12, 1943. Serial No. 498,370

. plurality of separate electrical impulses; another feature of this invention is that it provides a new system for providing indications of certain phenomena in an internal combustion engine, as the pressure variations due to detonation or knock" vof the fuel; still another feature of this invention is that itl provides improved means for elimin'ating the efiects'of'undesired variations; yet another feature oi' this invention is the provision of improved means for providing an initial adjustment of the indicating device, and for expanding or contracting the variation of the indicating devicefor a given pressure variationbeing' studied; and a further feature of this invention is that it provides an improved load and integrating circuit combination in association with a rectier tube. Other features and advantages of this inn vention will be apparent from the following specification and the drawings, in which:

Figure 1 is a block diagram of one form of this invention; and Figure 2 is an operative circuit diagram of the device shown schematically in Figure 1.

There are a number of types of test work where it is desirable to provide an indication of the average amplitude of a plurality of separate electrical impulses. One example is in connection with the determination of average pressure generated in a pump -or a cylinder of an internal combustion engine.. In suona case a pick-up or translating device may be used to translate the pressure variations into corresponding electrical variations. then these electrical variations or im- 'z claims. (c1. wzl-35) pulses may be used to actuate the indicating system. Such a system is used, for example, in determining the detonation characteristics of fuels.

Detonation or knock indications have heretofore been most commonly provided by a system employing a bouncing pin pick-up, operated by opening and closing contacts. The assignee of this ,application is now marketing a complete improved system for indicating detonation characteristics, this system being also adapted to other uses, as indicating pressure variations in pumps, or investigating substantially any type of intermittent electrical impulse. The particular pick'- up translates pressure variations in the cylinder under'test into corresponding electrical variations by varying an air gap in a magnetic circuit. The pick-up will not be described more fully here, as

`it is the subject of aco-pending application,

application Ser. No. 495,610, of- Ben R. Kamler and David L. Elam, which issued on March 19, 1946, as Patent No. 2,396,703.v

The particular embodiment of this invention which is illustrated in the accompanying drawings is for use vin test work on an internal com- 25 bustion engine, using a one-cylinder engine especially designed for such work and known as a CFR (Consolidated Fuel Research) engine. The detonation or knock frequencies whichare of particular interest in fuel testing are a function 3 of the cubical content of the cylinder under test,

usually rangingbetween 2,000 cycles per second (in large Diesel engines) an'd 10,000 or 20,000 cycles per second (in very small high speed engines), the knock frequencies in aV CFR engine 35 being very close to 6,500 cycles per second. The

the test engine, but -to eliminate undesired electrical variations. That is, if thetest engine is op` erating at 900 R. P. M., -the input ltothe illter would include vthe knock frequency at around 6,500 cycles perv second, the main explosion fref quencies at about cycles per second, and other Yundesired frequencies which might be due to valve knock, or the like. If the .fueldetonation frequencies are being studied, the nite'r I2 would betuned to about 6,500 cycles per second, and the other undesired frequencies would be eliminated. On'the other hand, if one wanted an average indication of the power` of the engine, this could be l Y secured by by-passing or disconnecting the lter I2, thereby obtaining an indication of the average 4 1,500 ohms and a decouplin condenser I3Ic with a capacity of 10 mfd. f i

The arrangement ju'stdescribed provides arelatively conventional resistance coupled ampliiler.

The only additional elements not heretofore described comprise the gid leak resistor I3m, which may have a value of l megohm,; and the variable volume control arrangement. f This arrangement comprises a variable resistance |311.' with an additional fixed resistance which may be sey lectively put in series with the variable resistor value of the main pressure forces in the engine. Y

The output 'of the tuner is delivered to amplifying meanrhere indicated as an amplifier IB.

integrator I4 comprising a rectifying tube and an integrating circuit averaging the voltage values.v

The averaged voltage is then delivered to a dump circuit' and used to actuate a knock meter I6, which may befa conventional milliammeter with an arbitrary scale. A power supply unit Yil? and voltage regulator I8 supply operating voltages andcurrents for the amplier I3 and integrator I4; anda completely separate bias control unit -I9 provides a variable bias voltage operating on the integrator for purposes to be hereafter more fully described. j

Referring now more particularly to'Figure r2, an operative` embodimentof the system schematically illustrated in Figure 1 will be described. The tuner I2 comprises a condenser I2a'in lseries with two inductances I2b and I2c, the output end ofthe latter inductance being connected to the signalI grid` ofthe iirst amplifying tube I3a. A point in the'connection between the inductances I 2b and I2c is connected to ground through the inductance IZd; and the output endl of the inductance I2c is connected to ground through a condenser I2e, the'condensers I2a and Ie being variable for tuning purposes. In a tuner designed Vfor fuel test work on automobile engines, for ex-` ample, the condenser elements IZa and i2e may have a maximum capacity of'.0018 mfd.; the inductances I 2b and I2ca valueof .6 h.; and the in ductance I2d a value of .045 h. This provides a two-stage tunable filter capable of covering a range of from about 4,500 to about 12,000 cycles per second, and particularly advantageous in that it effects the desired elimination without any loss in the strength of thevelectrical impulses; vin fact, the desired electrical impulses are actually amplied (due to resonance phenomena) in their passage through this particular tunable lter circuit.

The amplifier is shown as comprising two tubes i3d and I3b in cascade, with appropriate asso' ciated elements for-'operative circuit connections.

have arvaluegof 2,000 ohms, and the by-pass con` l densers i3d a'value of 50 mfd; .The screen grid resistors I3evmay lhavea value of .5 megohm;

andtheirby-pass condensers I3f a value of .11,

or short circuited by a 1 switch" |31). The lower variable resistance may have a maximum value of .5 megohm, and the upper nxed resistance avalue of 4.5 megohms. When the switchMinis-closed,l

the ampliiier gainis high; but when this switch is open, the amplier gain. level is relatively low,

regulated by the position ofthe contact arm onv the variable resistance; thejmaximumpossible Eainpwhen the switch is 'open being only llof that possible when itisclosed..l 1 f l The output of the second amplifying tube I 3b' A n is delivered through the couplingcondenser I3h vThe output of, this unit is in tum delivered to an to .a rectifying tube Ita which may, for example, be a 6H6 with its cathodes and-plates connected together, respectively, illustrated asv single ele-f ments here for simplicity. The 'cathode of this tube is connected to one end of a loadf resistor Mb. This resistance develops voltage variations in accordance with thev input to theintegrator.

and has in shunt with it a. condenservMc and a y combination of another resistorld'in series with a condenser Ide.V The resistances I4b and Idd may have a value of 5 megohms', .for example;

rand the condensers Idcand Ide aA value'of 2 mfd. These values are -high enough `.that the rst condenser and resistance providean integrating circuit with a time constant of about 10 seconds, the second condenser adding-'considerably more time factor to the integrating circuit. In addition, a third condenser M (which may also have a capacity of 2 mfd.) is adapted to be cut into the circuit when desired by an on-oiswitchV Mg. v All of these condensers and the lower end of the 'resistance I4b connect to a comof the coupling condenser I3h which is con iected to the plate element of the rectifying tube A variable bias voltage is applied to the point Mh. by the bias control means I9. :This includes a rectifying tube ita (whichmaybe another 6H6 with its cathodes and plates connected to.- gether, respectively, again illustrated assingle elements for simplicity) having its-cathodedirectly connectedv to one terminalof a standard 60 cycle 115 volt circuit, the plate being connected to `the other terminal through a` coupling condenser I9b which may have a= value of .05 mfd.

The rectified output is developed across two series resistances I9c land I9d. The Aupper. orpxed remfd.. The'plate load resistorsV I3g may have a value of .15' megohm, and the coupling condensers |311. a value of .0015 mfd. vThe plate voltage sup-y ply. may'include a resistor I3 with a value of sistor may have a value4 of 30,000 ovlims'and the lower variable resistance avalueof 50,000 ohms. The lower end of the variable resistance orfpotentiometer is connectedy to ground" niiany` de- 1s'takenl o siredl bias voltage (abovegrou'nd l through the movable contactarmypa'ssed thr'ogh a lterresistance I9e, and `einzu'iected'tcf the point Mh. to give it the desired.biasfvcltagevwith.respect to ground. The condenserf'lffof relanection of theA load resistanceMt-(whichmay characteristics (unknown octane number).

have a value of about 500,000 ohms) between this point and the plate of the rectifier tube is particularly important. The normal circuit would have the load resistor Ill connected from plate to ground: but we have found that this provides an inferior circuit as compared with the'arrangement shown.

`ll'he output of the integrator I4 is delivered to lthe dump cricuit I5. In particular, the output of the integrator is connected to the grid of a three element tube Ia, which may be a 6F5. The cathode of this tube is connected to ground through a variable resistance lib and the knock meter I6. Since the maximum space current of a 6F5 is low, the knock meter may be a milliam'- meter with a maximum deflection of 1.2,5 milliamperes. Preferably, the scale is divided in an arbitrary manner, as in units from 1 to 100. The variable resistance I5b would, in the present case, have a maximum value of about 5,000 ohms;v and this variable resistance operates as a spreader to control the amount of deflection of the needle of the meter per unit of electrical input to the tube Ita. No by-pass condenser should be used, as all of the variable currents in the plate circuit should pass through this resistor.

All of the tubes in the system are suppliedwith operating voltages in relatively conventional manner. The cathodes are heated by a low voltage circuit directly tapped off of a transformer, this circuit not being shown since it is conventional and would confuse the showing of the novel portions of the circuit. Plate voltage is developed in a power supply unit I1, passed through a voltage regulator and filter I8 and delivered to the plate elements of the various tubes having three or more elements. In order to get the best possible voltage regulation, the commercial current is first passed through a voltage regulator unit 20 of conventional type available on the commercial market. The stabilized output of this unit is then delivered (when the switch IIa is closed) to the primary of the transformer IIb, the high voltage secondary of this transformer having its center tap connected to ground and its ends connected to the two plate elements of a rectifying tube I'lc, which may be a 5Y3. The rectied output is delivered through a blocking resistor Ild, which may have a value of 3,000 ohms, to the input of a final voltage regulator and filter unit. This unit has two voltage regulating tubes I8a and I8b (which may be type 150 VR. tubes) in series, the mid-point being connected to ground through a resistance I8e, which may'have a value of .2 megohm. A choke coil I8d is in series with the output: and two con-S densers Ie and I8f (which may each have a value of 10 mfd.) are connected between the input and output, respectively, and ground.

As representative of one use to which this equipment may be put, thevprocedure will be described for'testing a gasoline of unknown knock The operator would rst start the CFR engine I I with a standard fuel of known octane number, Va fuel which he believes to be somewhat similar in octane characteristics to that to be tested. He would then close the shorting switch I2f. so that there would be no signal input to the apparatus, turn the spreader rheostat I5b to minimum (0) value, and adjust the bias voltage (through variation of the control ofthe potentiometer I9d) until the indicating needle of the knock meter t9 stood at zero.

'I'he switch I2! would then be open and the engine compression (or some other factor) adjusted until a knock was heard with the ear. The variable condensers I2a and I2e in the tuner 5 would then be adjusted to-give the maximum reading on the knock meter, initial tuning being done with the volume control at maximum gain (switch Ipclosed), and final tuning being done with this switch open and the control of the variable volume control resistance |311. at a'position keeping the meter needle near the center of the dial. The condensers are not ganged, since it is desirable to be able to make independent adjustments of the condenser I2a with different pickups having different inductive characteristics; but the' dials of these condensers are preferably calibrated in frequency to enable an initial adjustment to approximately the correct position. With the tuning completed and set at the proper position, as indicated by response of the knock meter, the spreader rheostat I5b is adjusted to a selected position determined by the engine and fuel under test, the volume control is adjusted to bring the meter needle back to midscale position on the dial, the switch I4g closed to throw in the'last condenser Ilf in the integrator, and the test engine II switched over to the unknown fuel. The knock meter needle will then either go up on the scale (indicating the unknown fuel to be of lower octane rating-more knockthan the known fuel), or go down on the scale (indicatingthe unknown fuel to have a higher octane rating). The actual octane rating of the fuel is determined from a combination of various characteristics, including the horsepower output of the test engine, but with theother conditions all held constant the knock meter can be calibrated directly in octane rating. Rather, the arbitrary unit on the meter can be related to a chart to directly determine the octane rating under various conditions.

For example, if the standard fuel had an octane rating of 70, and it were known in advance that the unknown fuel had a higher octane rating, the

45 volume control could be adjusted to have the indicator needle 'stand at full scale (100 units) when the test engine II is running on the known fuel. With all of the spreader rheostat resistance I5b in circuit, if switching the test engine BG II over to the unknown f uel causes the meter needle to drop from 100 to 85, the octane rating of the unknown fuel is '72.A On the other hand, if the spreader rheostat I5,b were adjusted to maximum spread position (all resistance cut out),

5s switching from the known fuel tothe unknown fuels (where the known fuel is 70 octane and the unknown is 72 octane) causes the meter needle to drop from 100 to 30.

It will be apparent that the provision of the y spreader rheostat I 5b, the variable bias voltage control unit I9, and the variable volume control arrangement provide considerable flexibility, taking full advantage of the integrating or averaging ability of the integrator I4. By proper handling of these controls the apparatus may be protected when an unknown fuel is first being investigated; yet very minute differences in detonation characteristics may be examined and will provide a considerable change in the meter readlng if the rheostat I5b is set at maximum spread position.

The spreader resistance I5b operates as aselfbiasing control, rather than by reason of the addition or subtraction of resistance. The maximum resistance of this element is 5,000 ohms,

l whereas the plate resistance of the tube lia would i normally be 100,000 ohms or more, so that it would be apparent that a change of a few hundred ohms resistance in the circuit would make no appreciable difference in current iiow by rea- 4 1 son of the resistance variation as such.

Increasing the resistance of the element lib,

. however, causes additional bias voltage to be developed across it (by reason of the flow of plate "current therethrough), which adds to the bias voltage delivered by the unit I9 to result in a smaller plate current flow through the meter for a given input voltage from the pick-up I0. That is, the bias voltage provided by the unit. I9 del termines the initial point f current flow in the l tube Ia; while the amount oi"` resistance in circuit with the cathode determines the self-biasing or A. C. biasing effect. The higher the resistance l (up to a limiting value) the greater will be the reduction in meter plate current flow per unit of voltage variation in the signal above the initial point set by the other bias means.

This additional bias voltage permits a selection of any meter' spread per given single octane'number difference in fuel from about eight to about Changes,A therefore, in the construction and arl rangement may be made without departing from the-spirit and scope of the invention as disclosed in the appended claims.

We claim: 1. Apparatus of the character described for providing a desired indication of phenomena occur- ,ring during the operation of an internal combustion engine from impulses derived from means for translating periodic pressure variations 'in F said engine into corresponding electrical impulses, including: means for amplifying said impulses and eliminating undesired electrical variations; a rectifying tube having at least plate and cathode elements; an integrating circuit comprising a first resistance element and a rst condenser element in shunt, the first resistance element being in series in the plate-cathode circuit of said rectifying tube, and asecond resistance element and a second condenser element in series with each other and in shunt with the first elements,

the impedance of said elements being sufficiently n high to provide a time constant many times higher than the time interval between said impulses, .whereby the voltage across the second condenser element is a function of an average of said im-` pulses; av tube having-at least grid, plate, and cathode elements; means for applying said voltage to the grid vof said tube, whereby the space current in the tube is a function of said voltage;

indicating means actuated by said space current;

and means for varying the response of said indicating means.

2. Apparatus of the character claimed in claim -1, including means for supplying a bias voltage to one of said tubes, this means being variable lto enable initial adjustment of the indicating means.

3. Apparatus of the character claimed in claim 1, including power supply means for energizing said amplifying means and tubes, and separate means for supplying a bias voltage to the grid vof the last mentioned tube, this means being vari' able to enable initial adjustment of the indicating means.

4. Apparatus of the character described for providing a desired indication of a variable voltage, including: a tube having at least grid, cathode and plate elements; means for applying said voltage to the grid of said tube, whereby the space current in the tube is a function of the voltage; indicating means actuated as a function of said space current; variable means for applying a bias voltage to one ofthe two first-mentioned elements of said tube which is independent of the variable voltage and space current; and variable means for applying a bias voltage to one of the-two first-mentioned elements of said tube 4, wherein the last mentioned means comprises I a variable resistor in series with the cathode, the circuit being so arranged that all variable currents in the plate circuit pass through this resistor..`

6. Apparatus of the character described for in'- dicating the average amplitude of a plurality of electrical impulses, including: means for amplifying said impulses; a rectifying tube having at least plate and cathode elements; an integrating circuit comprising a first resistance element anda rst condenser element in shunt, the rst resistance element being in series in the plate'- cathode circuit of said rectifyingl tube, and a second resistance element and a'second condenser element in series with each other and in shunt with the first elements, the impedance of said Yleast grid, plate, and cathode elements; means for applyingsaid voltage to the grid of said tube, whereby the space current in the tube is a function of said voltage; indicating means actuated by said space current; and means for supplying a bias voltage to the end of the rst resistance' furthest from the cathode element of the rectifying tube, a connection from the amplifying means being made to the plate element of the rectifying tube and a return connection to said amplifying means being made through said shunt elements and through the bias means.

7. Apparatus of the characterdescribed for indicating .the average amplitude of a plurality of electrical impulses, including: means for ampliL fying said impulses; a rectifying tube having at least plate and cathode elements; an integrating circuit comprising a first resistance element and a first condenser element in shunt, the first resistance element being in series. in the platecathode circuit of said rectifying tube, and a second resistance element and a second condenser element in series with each other and in shunt with the first elements, the impedance of said elements being suiliciently high to provide a time constant many times higher than the time interval between said impulses, whereby the voltage' .across the second condenser element vis a function of an average of said impulses; a third resistance element connected between the plate element of the rectifying tube and the end of the first resistance element furthest from the cathode element thereof, the connection from the amplifying means being made to a point between the plate element of the rectifying tube and the adjacent end of the third resistance element; a tube having at least grid, plate, and cathode elements; means for applying said .voltage to the catlng means actuated by said space current.

ALFRED oaossLEY. D. L. mM.

REFERENCES curan The following references are of record in the me of this patent:

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'20 Beale and Stansileld, published in "The Englneer, Dec. 27, 1935, -pages 667-669.,

(Copy 1x1 177451.11.) 

